Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

The primary ions strike the target in randomly distributed points of its surface, potentially leading to the creation of surface roughness. The first involves exploring the variation in density near surface target which is challenging to measure. The second focuses on observing alterations in the surface topography of the target by measuring the amount of deformation in the geometric structure. This brief work is clearly needed to clarify the first approach by adopting the feasible expressions to establish the dependence of the range straggling, energy and dose of ions beam on the basic mechanisms leading to surface roughness by introducing new parameter described the unchanged surface density rate. This parameter predicts the frequency of presence roughness phenomena. The results of our simulations performed for an amorphous target are in perfect agreement with experimental results obtained by Wach et al.

The penetration of corrosion into the volume of the copper coin of Euthydemus I and the fragments of rings from the Uzundara fortress was studied by the methods of neutron radiography and tomography using a facility installed on the horizontal beamline of the WWR-SM nuclear reactor of the Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan. Three-dimensional models of the studied archaeological objects were reconstructed, and the volume fractions of the initial metal and corrosive materials were calculated. A large number of pores and cavities were found inside the volume of the coin, which may indicate a violation or imperfection of the casting technology, as well as active chemical processes due to the interaction of the coin with the soil. X-ray diffraction studies have established the presence of phases of copper, cuprite Cu₂O, and nantokite CuCl on the surface of the Euthydemus I coin. According to neutron tomography data, the volume content of copper and corrosion products was determined to be 1469.93(2) and 169.04(2) mm³, respectively. The distribution of pores in the volume of the Euthydemus I coin by an equivalent diameter has also been established. Two rings were studied at the neutron radiography and tomography facility; the volume of the first ring was 1491.17(6) mm³, and the volume of a certain corrosion was 135.69(7) mm³. On the second ring, the corrosion volume was 373.67(3) mm³, which is 12.1% of the total ring volume.

Surface morphology features of dense palladium-based membrane filters are studied using atomic force microscopy and scanning electron microscopy methods. Elemental compositions of the filters are Pd₉₅Pb₅ and Pd_93.5In_6.0Ru_0.5 (hereafter, numerical coefficients mean the composition in wt %). The thickness of the dense membrane filters is 50 and 70 µm, respectively. High-purity metal samples are obtained by methods of electric arc fusion in a protective atmosphere and cold rolling with intermediate vacuum annealing. There are differences in morphology of the filter surface due to the elemental composition of the alloys. Manifestations of cavitation in the form of µm-sized funnels are found upon palladium doping with lead, and there are no such funnels for palladium alloyed with indium and ruthenium. Differences in the surface roughness of the samples are revealed. Surface areas of different hardness are detected using atomic force microscopy in the lateral force contrast mode. The obtained results are important not only for the choice of material for the manufacture of membrane filters with improved performance characteristics but also for the development of the elemental composition of membrane filters in order to optimize their operation in high-tech modern technological processes.

The paper presents the results of a theoretical study of the electronic structure and electrical conductivity of single-walled gold nanotubes with chirality indices (4, 0), (5, 0), (6, 0), (7, 0), (4, 4), and (5, 5). The simulations were performed using the density functional theory and the method of nonequilibrium Green’s functions. The Perduew–Burke–Ernzerhof exchange-correlation functional and a two-exponential basis set were used. The importance of using polarized basis sets for the study of electrical properties of gold nanotubes is demonstrated. Analysis of the results showed that the transmission functions of the studied nanotubes depend on their structure in a complex way but, in general, increase with increasing diameter. The dependence of the transmission function on the electron energy does not allow us to speak a priori about the linearity of the current–voltage characteristic of gold nanotubes within a certain finite voltage range. In addition to defect-free single-walled gold nanotubes, gold nanotubes of different diameters with a vacancy-type defect-were also studied. This allowed us to evaluate the effect of such a defect on the atomic structure and electrical conductivity of the single-walled gold nanotubes. It was demonstrated that the conductivity drop can vary within a wide range, correlating with changes in the atomic structure.

The possibility of replacing iron with cobalt in iron disilicide is studied. It has been shown that, in a wide range of compositions, an attempt to replace iron with cobalt leads to the formation of cobalt silicides. Using the composition Fe_0.98Co_0.015Si₂ as an example, it is shown that during the directional crystallization and subsequent annealing of samples, a regular microstructure is formed. Anisotropy of thermoelectric properties is observed along and across the crystallization axis of the sample. In the region of low cobalt concentrations, upon transition to pure β-FeSi₂, the sign and magnitude of thermopower change sharply.

We present high precision determination of electron energy loss functions and thereby the optical constants, n and k, of solids from the measured, high energy resolution reflection electron energy-loss spectroscopy (REELS) spectra, covering the spectral energy range from visible to vacuum ultraviolet. The calculations are based on our recently developed reverse Monte Carlo (RMC) method. The RMC method combines a Monte Carlo modelling of electron transportation for REELS spectrum simulation, including both the elastic and inelastic collisions, with a Markov chain Monte Carlo calculation of parameterized energy loss function, Im [–1/ε(ω)]. We found that our calculated optical data of elements fulfill the sum rules with very high accuracy; therefore, the use of this calculated optical data in material science and surface analysis is highly recommended for further applications.

The temperature dependences of the structural parameters of thin films of polystyrene–fullerene C₆₀/C₇₀ nanocomposites with a low content of nanoparticles in the vicinity of the glass transition temperature of the polymer matrix were studied by specular neutron reflectometry in the range of 15–150°C. The obtained temperature dependences of film thickness were used to estimate the glass transition temperature of film composites. In the case of films with C₆₀ fullerene, the dependence had a standard form. The glass transition temperature of the composite film was found to decrease compared to the known value for the pure bulk polymer. In the case of films with C₇₀ fullerene, upon transition to high temperatures, a nonmonotonic dependence of the film thickness was observed, which hindered application of the general approach.

A model of the structure of thermally modified shungite carbon is proposed, which can be used as a container for the production and long-term retention of nanosized particles. Such nanoparticles are characterized by their inherent photoluminescence activity. Since nanosized carbon particles do not enter into chemical interaction with the shungite matrix under normal conditions, their luminescent properties are maintained for a long time. The description of the multilevel structure of shungite carbon by the model of randomly oriented agglomerations of turbostratic stacks of graphene sheets is confirmed by X-ray studies.

The results of a study of the combined effect on the W–Cu pseudoalloy of pulsed flows of deuterium ions with a power density of q_i ≈ 1 × 10⁹ W/cm² at an exposure duration of τ_i = 20 ns and deuterium plasma with parameters q_pl ≈ 1 × 10⁸ W/cm² and τ_pl = 20 ns generated in the “Vikhr” Plasma Focus installation are presented. It is shown that in the implemented mode of irradiation the nature of the damage to the surface layer of the tested material depends on the state of the surface of the irradiated samples and the number of pulsed impacts of energy flows. The impact of pulsed irradiation on the polished surface of pseudoalloy samples leads to the appearance of extended copper drops on the tungsten surface and to the formation of many pores, which are observed both in Cu drops and in the W matrix. In addition, microcracks appear on the W surface, as well as islands of a copper film of arbitrary configuration. Repeated irradiation of samples of the studied material with an unpolished surface leads to the formation of chains of tungsten droplets located in the upper parts of extended ridges formed during grinding of the original samples. Bursting bubbles are also visible on the irradiated surface, which arise as a result of the boiling of copper inclusions and a copper film deposited on tungsten. Clusters of such bubbles are often localized along ridges on the tungsten surface. The results obtained are discussed using numerical calculations and analysis of the thermal effect on the considered pseudoalloy under pulsed irradiation.

We investigate the processes of microrelief formation on a Si(100) surface under irradiation with a Ga⁺-ion beam with an energy of 30 keV and a fluence of D = 1.25 × 10¹⁸–2 × 10¹⁹ cm^–2 at incident angles of θ = 30°–85°. Within the angular range of θ = 40°–70°, a faceted wavy relief forms on the Si surface, while at θ = 30°, a sinusoidal relief develops. An experimental dependence of the periodic structure wavelength as a function of irradiation time λ(t) ~ t ⁿ, where n = 0.33–0.35, is obtained. The average values of relief propagation velocities and their direction relative to the incident ion direction are determined for θ = 30° and 40°, amounting to –5.3 ± 0.6 and –6.3 ± 0.6 nm s^–1, respectively. The results are discussed in detail within the framework of existing models of wavelike surface relief formation under ion bombardment.